Something

using System.Text;
using NHibernate.Mapping.Attributes;
using NHibernate;
using NHibernate.Cfg;

namespace Pcms.Classes
{
    [Class(Table="[Group]")]
    public class Group
    {
        private int _groupID;
        private string _name;
        private int _userID;

        [Id(0, Name = "GroupID", Type = "Int32", UnsavedValue = "0")]
        [Generator(1, Class = "identity")]
        public virtual int GroupID
        {
            get { return _groupID; }
            set { _groupID = value; }
        }

        [Property(Type = "AnsiString", NotNull = true, Length = 50)]
        public virtual string Name
        {
            get { return _name; }
            set { _name = value; }
        }

        [Set(0,Name = "UserID", Table = "User", Lazy = true, Cascade = CascadeStyle.SaveUpdate)]
        [Key(1,Column = "GroupID")]
        [ManyToMany(2,Class = "Group")]
        public virtual int UserID
        {
            get { return _userID; }
            set { _userID = value; }
        }
    }
}